1. Field of the Invention
The present invention relates to a contact for a vacuum interrupter which has excellent characteristics of high withstand voltage, low melting bonding property, large current durability and low chopping current.
2. Description of the Prior Arts
The important characteristics of a contact for a vacuum interrupter include:
(1) high interrupting property of a current interrupter; PA1 (2) high withstand voltage; PA1 (3) small contact resistance; PA1 (4) low melt bonding property; PA1 (5) low erosion of a contact; and PA1 (6) small chopping current.
It has been difficult to obtain a contact which is practically used and has all satisfactory characteristics. Accordingly, it has been considered to use a contact which has certain important characteristics even though the contact has inferior characteristics for other features depending upon its usage for a vacuum interrupter.
For example, a copper-bismuth alloy (Cu-Bi) has been mainly used for a contact for a vacuum interrupter.
According to our experience, a contact made of the Cu-Bi alloy containing less than 0.5 wt.% of Bi has large chopping current whereas a contact made of the Cu-Bi alloy containing more than 0.5 wt.% of Bi has relatively low withstand voltage.
When the chopping current is large, there is a possibility to cause abnormal voltage between contacts. When the withstand voltage is low, the contact can not be used in a high voltage circuit.